The proposed studies will be along two lines of enquiry. The first will be the development of an endocrine kidney transplanted to the neck of sheep. This model will eliminate the renal excretory function leaving only the endocrine function of the kidney intact. Animals thus prepared will be used to study the development of renal hypertension by narrowing the renal artery to the endrocrine and/or normal in situ kidney. Changes in renin secretion, renin substrate concentration and kinetics of the renin-renin substrate reaction will be measured. The endocrine kidney model will also be used to study the antihypertensive role of renal tissue without excretory function and a possible pressure sensitive receptor for this antihypertensive function. In addition, studies on the dynamic response of the vascular receptor for renin secretion and a possible role for the macula densa in the synthesis and storage of renin will be studied in this model. This model will also be developed in dogs so that species differences can be compared. The second line of enquiry will deal with the role of the macula densa in renin secretion. These studies will be performed in conscious sheep previously surgically prepared. The effects of renal artery administration of ouabain and ethacrynic acid singly and in combination will be studied to better understand the role of transcellular movement of sodium plus chloride and homocellular movement of sodium plus potassium as well as changes in intracellular sodium concentration on the control of renin secretion by the macula densa. Relevant pressure related variables including, renal resistance changes and flow pulse profile will be measured to ascertain if the vascular receptor for renin secretion could be contributing to the observed changes.